1. Field of the Invention
The present invention relates to fluorinated polyethers having low optical propagation loss, small optical birefringence, and a precious refractive index controllability, as well as a method of preparing the fluorinated polyethers and a use of the fluorinated polyethers for the fabrication of core and cladding layers of waveguide type optical devices, such as a thermo-optic switch, an optical splitter, a variable optical attenuator, a polarization splitter, tunable and fixed wavelength filters and arrayed waveguide gratings, etc.
2. Description of the Prior Art
High performance polymer materials, such as those used in planar waveguide type optical devices and optical interconnectors, require high thermal and environmental stabilities, low optical propagation loss at optical communication regions of 1.3 μm and 1.55 μm, precise refractive index controllability, adaptability to various substrates, feasibility of multi-layer thin film, dimensional flexibility, easy alignment with micro optical components, and basically cost effective technology.
Fluorinated poly(arylene ether), which were originally developed for use as low dielectric materials in semiconductor processes, have an potential applicability as an material for optical devices by virtue of its excellent thermal and mechanical characteristics and low moisture absorption (See, U.S. Pat. No. 5,115,082). However, the fluorinated poly(arylene ether) disclosed in the patent has a significantly insufficient chemical resistance and thus cannot be used for fabricating the optical devices by a multi-layer thin film fabrication process.
In an attempt to overcome the problem with the fluorinated poly(arylene ether), Korean Patent No. 226442 discloses a fluorinated poly(arylene ether) having a thermosettable acetylene end group. The polymer disclosed in this patent can provide a thin film having an excellent chemical resistance by a thermal cross-linking process and can be used applied to fabricate the optical devices. However, the fluorinated poly(arylene ether) is disadvantageous in that it is high in optical birefringence as it has an intrinsically aromatic, rigid rod-like molecular structure. Also, the aromatic fluorinated poly(arylene ether) has a refractive index of 1.50 or above at a wavelength of 1550 nm, which is significantly different from that of optical fibers (1.46). For this reason, the polymer has high reflection loss at an interconnection with the optical fibers.